This invention is directed to drilling rigs and specifically involves a highly mobile back-in type self-propelled rig which has the capability of transporting a telescoping mast which is tall enough to pull and rack sections of drillpipe in three-joint lengths.
Standard drillpipe normally is manufactured in thirty foot joints and there are mobile drilling rigs available in the art which are capable of handling drillpipe sections two-joints in length. These involve the single trailer rig, the double trailer rig, and the truck mounted rig. With the single trailer rig, a semi-trailer is utilized to carry the entire rig apparatus including the telescoping mast, the drawworks, and the power supply. Due to highway weight limitations on the amount of weight allowed per set of axles, the largest mast that may be utilized on a single trailer rig can only handle drillpipe in two-joint lengths. The same is true for the truck mounted rig which uses a single extended truck chassis to transport the rig components.
The double trailer rig utilizes one trailer to carry the mast and accompanying equipment and a second trailer to carry the engines and drawworks. The dual trailer rig uses two trucks to pull the trailers and actually comprises two truck-trailer combinations.
Neither the single trailer rig nor the truck mounted rig can carry a mast large enough to pull three-joints or ninety feet of drillpipe at a time due to the legal weight limitations on the axles. The dual trailer rig may be capable of carrying a large enough mast but essentially requires two separate vehicles to transport it.
The present invention provides a single portable vehicular rig having a mast-carrying capability sufficient to legally transport a mast which can handle three-joint sections of drillpipe. This is particularly advantageous because of the fast rig operation resulting from the ability to handle three-joint sections of drillpipe rather than only the two-joint sections to which the prior devices are limited. This results in a reduction of approximately 33 percent in the number of times the drillpipe joints have to be made-up or broken out when going in or coming out of the hole. This is achieved by using a jointed or articulated self-propelled rig with a unique swivel joint which allows three sets of axles to distribute the weight, as opposed to the two sets of axles on the prior rig vehicles.